Device for transmitting data in a motor vehicle

ABSTRACT

A device for data transmission in a motor vehicle and/or from a motor vehicle in its vicinity includes a first transceiver unit in or on the motor vehicle and a second transceiver unit. which is provided in at least one transponder unit whose spatial position relative to the vehicle may be variable or any desired position. In the first transceiver unit is a radar unit equipped for distance measurement, expanded by adding a two-channel data transmission system. The second transceiver unit is also a two-channel data transmission unit, and the microwave frequencies for two-channel communication of the data transmission system are selected so that their difference yields an intermediate frequency which is processable using conventional components in a heterodyne receiver in the reception part of each of the first and second transceiver units.

FIELD OF THE INVENTION

The present invention relates to a device for data transmission in amotor vehicle and/or from a motor vehicle in its vicinity, including afirst transceiver unit in or on the motor vehicle and a secondtransceiver unit which is provided in at least one transponder unitwhose spatial position relative to the vehicle may be variable or anydesired position.

BACKGROUND INFORMATION

Such a device is discussed in IEEE Transactions on IndustrialElectronics, Vol. 35, No. 2, May 1988 under the title “Keyless entrysystem with radio card transponder.” This data transmission devicetransmits a coded query sequence via an induction loop mounted on thevehicle, e.g., in an exterior mirror or in the bumper, to a transponderaccommodated in a card the size of a credit card, which then delivers aresponse sequence via an antenna. The transmission frequencies used hereare in the range of a few hundred kHz.

In general, the mechanical keys customary in the past are currentlyincreasingly being replaced by electronic systems such as remote controlsystems using infrared or wireless signals for access authorization tovehicles. In other words, electronically encoded keys are being used toan increasing extent for startup authorization.

Communication systems between vehicles and an infrastructureinstallation, e.g., for acquisition of road use fees, are also referredto in other prior systems.

Also referred to in other prior systems are radar distance measuringsystems which are installed in the vehicle and operate in the gigahertzrange and a radar sensor on at least one side of the vehicle formeasuring the distance and velocity between the vehicle and an obstacle,e.g., a vehicle driving in front or a parked vehicle.

SUMMARY OF THE INVENTION

It is an object of the present invention to utilize in a simple manner aradar transmission channel, which is present in the vehicle for distancemeasurement, for other data transmission functions which are activatedonly in conjunction with a data exchange which is deemed valid. Firstly,this should reduce costs in manufacturing these systems in comparisonwith previous separate radar and data transmission systems, andsecondly, the security of the transmission between the vehicle and oneor more transponders should increase.

Therefore, in order to achieve the object formulated above, a wirelessconnection is established between the vehicle and at least onetransponder. A particular simplification combined with a simultaneousincrease in security is achieved due to the fact that each transceiverunit includes a two-channel data transmission unit whose microwavefrequencies for two-channel communication are selected so that theirdifference yields an intermediate frequency which is processable byusing conventional components in a heterodyne receiver of the receivingpart of the first and second transceiver.

The orientation of the transmitting and receiving antennas relative toone another is problematical because the spatial position of thetransponder, in particular, the key (i.e. key fob) to the vehicle isvariable as desired. For example, the key may be in the driver's pantspocket.

If a linearly polarized antenna is used in the vehicle sensor and acircularly polarized antenna is used in the transponder to achieve thisgoal, this avoids the case of two linearly polarized antennas whichwould produce a theoretically infinitely high attenuation of thetransmitted signal if their polarization directions were at rightangles.

Furthermore, one or more antennas having the most spherical, i.e.,omnidirectional characteristic should be used in the transponder (key).

The radar sensor of the vehicle used for measuring distance and velocityis expanded by adding a two-channel data transmission system which maybe used for local communication with a key for “keyless entry”applications and also for communication with an installation foracquisition of fees, for telematic applications or other remote controlapplications.

The two transceivers are configured so that their oscillator signal (LOsignal) is used for downmixing in the case of reception. Thetransmission frequency and the receiving frequency are such that theband limits of the frequency band used may be upheld due to the theirfrequency shift. Therefore, frequency stabilization need be used on onlyone side, i.e., on the motor vehicle side or on the transponder side.Therefore, and due to the fact that conventional components may be used,the entire data transmission system may be implemented inexpensively.

The exemplary data transmission device according to the presentinvention is explained in greater detail below on the basis of theenclosed drawing using exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in the form of a block diagram a first exemplary embodimentof the data transmission device according to the present invention inwhich the transponder side includes an AFC circuit which pulls thefrequency of an oscillator, which may be a dielectric resonantoscillator (DRO) for example, so that the intermediate frequency is keptconstant.

FIG. 2 shows a second exemplary embodiment in the form of a blockdiagram in which the intermediate frequency, which fluctuates due to thefrequency drift of the DRO, is compensated by the fact that a variableLO signal is generated in the receiving branch and downmixes theintermediate frequency to a lower constant intermediate frequency.

FIG. 3 shows in the form of a table the additional attenuation resultingdue to a difference in polarization between the field and the antenna.

FIG. 4 shows a transmitting/receiving antenna including a directionalcoupler.

FIG. 5 shows a block diagram of the part of the data transmission devicelocated in a vehicle, the data transmission device is integrated-into anexisting automotive radar sensor.

DETAILED DESCRIPTION

FIG. 1 shows a first exemplary embodiment of a two-channel datatransmission device according to the present invention in the form of ablock diagram. On the left side of a vertical line indicated with adash-dot line, the vehicle side including a first transceiver unit 1 isillustrated, and on the right side of the dash-dot line the transponderside including a second transceiver unit 2 is shown. First transceiverunit 1 in or on the vehicle includes a dielectric resonant oscillator(DRO) 10 whose oscillator frequency f₁ (first frequency) is modulated bya transmission modulator 11 using a coded sequence, e.g., in the form ofan ASK (amplitude shift keying) modulation. Instead of this, an FSK(frequency shift keying) or PSK (phase shift keying) modulation may beused. In the receiving branch there is a heterodyne receiver including amixer 12, a low-pass filter 13 and a demodulator 14. A first antenna 15of first transceiver unit 1 is a transmitting antenna 15 which transmitsa signal having frequency f₁. A second antenna 16 is a receiving antennawhich receives a signal having frequency f₂ from the transponder. Mixer12 mixes the received signal having frequency f₂ with transmissionfrequency f₁ of DRO 10, and intermediate frequency f_(IF) is formed fromdifference |f₁−f₂| after low-pass filtering 13. The reception signal inintermediate frequency position f_(IF) is then demodulated bydemodulator 14. The two frequencies f₁ and f₂ are selected so that theirdifference |f₁−f₂|, i.e., intermediate frequency f_(IF), may beprocessed with inexpensive conventional standard components.

Due to the conventional and inexpensive implementation of the microwaveoscillator with a dielectric resonator (DR), there is a certainfrequency drift without stabilization measures. For this reason, asafety margin from the band limits is selected for thetransmission/receiving frequencies and this yields a certain frequencyshift and thus an intermediate frequency f_(IF).

On the transponder side, the transmitting branch of second transceiverunit 2 also includes a dielectric resonant oscillator DRO 20 and amodulator 21 which modulates it. Transmission frequency f₂ generated byDRO 20 and modulated by modulator 21 is sent over a power splitter totransmitting antenna 26 of second transceiver unit 2. The reception partof second transceiver unit 2 includes a heterodyne receiver which inturn includes a mixer 22, a low-pass filter 23 and a demodulator 24.Frequency f₂ of DRO 20 is downmixed in mixer 22 with modulated signal f₁received by first transceiver unit 1, forming intermediate frequencyf_(IF)=|f₁−f₂| which is demodulated in demodulator 24 after low-passfiltering in low-pass filter 23.

The converse case, i.e., when the transmitting branch in secondtransceiver unit 2 transmits and the receiving branch in the firsttransceiver unit receives on the vehicle side, functions in the samemanner. Full duplex operation is thus allowed, each of the twotransceiver units 1 and 2 are active.

The only difference between the two transceiver units is that onecontains the frequency regulation so that the frequency shift caused byusing DROs is compensated, and the intermediate frequency is keptconstant. In the exemplary embodiment in FIG. 1, second transceiver unit2 includes an AFC circuit 27 on the transponder side, “pulling”frequency f₂ of DRO 20, so that intermediate frequency f_(IF) is keptconstant. Therefore, DRO 20 of second transceiver unit 2 conforms to thefrequency drift of first DRO 10 on the vehicle side.

On the vehicle side, the exemplary embodiment illustrated in FIG. 2 isidentical to the exemplary embodiment described above and illustrated inFIG. 1. Only the reception part of second transceiver unit 2 in thetransponder has been modified in comparison with the exemplaryembodiment in FIG. 1. Intermediate frequency f_(IF) which fluctuates dueto the frequency drift of DROs 10, 20 is compensated according to FIG. 2by the fact that it is not regulated but instead it is mixed down with avariable local oscillator signal f_(LO) to a lower constant intermediatefrequency f_(IF2). To do so, a local oscillator 28, a mixer 30 and alow-pass filter 29 are used in addition.

The problem in orientation of transmitting/receiving antennas 15, 16,27, 26 of the first and second transceiver units is explained below onthe basis of FIG. 3.

Copolarized antennas are normally used in wireless transmission systemson the transmitting and receiving sides and are usually linearlypolarized. For example, if two dipoles are used, a maximum signalstrength at the receiving dipole (attenuation 0 dB) is obtained with aparallel orientation. If the two dipoles are rotated 90° toward oneanother, the attenuation is (theoretically) infinitely great. These twocases are illustrated in the table in FIG. 3. However, since there isalways some reflection in the vicinity of the antennas, a weak signal isnevertheless received in practice.

If one antenna is circularly polarized (circularly anticlockwiserotating or circularly clockwise rotating) and the other antenna islinearly polarized, then in the best case the signal attenuation amountsto 3 dB, depending on how the antenna is rotated in its planeperpendicular to the direction of the connection.

Both antennas should not be circularly polarized because if anon-omnidirectional antenna is oriented in the direction opposite thatof the other antenna, reflection results in the direction of rotation ofthe circularly polarized waves being in the opposite direction, and theattenuation being (theoretically) infinitely great.

In a passive entry system made possible by the exemplary datatransmission device according to the present invention, the position ofthe vehicle is assumed to be fixed in space, but there may be anydesired orientation of the transponder to the vehicle, so a linearpolarization should be used on one side and circular polarization on theother side. Therefore, it is not possible for the case of theoreticallyinfinitely attenuation to occur. According to the present invention, thepassive entry system is implemented in the microwave range. Then thehigh-frequency front end in the vehicle may be provided, for example,with a linearly polarized patch antenna, and an array of one or morecircularly polarized patch antennas may be used in the key with thetransponder to obtain the best omnidirectional characteristic.

In departure from the two implementations indicated schematically inFIGS. 1 and 2 in which one transmitting antenna each is providedseparately from a receiving antenna on both sides of first and secondtransceiver units 1 and 2, also a monostatic implementation including adirectional coupler may be used. Such an implementation is illustratedin FIG. 4. The receiving branch is connected to the transmitting branchvia a directional coupler, and the transmitting/receiving antenna iscommon to both branches.

FIG. 5 shows details of a data transmission device implemented on thevehicle side and combined with an existing automotive radar sensor. Forthe “data transmission” mode of operation, both high speed switches HSS₁and HSS₂ are closed by being driven not by snap-off diodes but insteadby a direct voltage. The other function blocks of the data transmissiondevice are identical to the components of transceiver unit 1 of FIGS. 1and 2.

The required AFC circuit (FIGS. 1 and 2) is integrated into thetransponder, i.e., in second transceiver unit 2 in the key fob, in abeacon, etc., because this transceiver unit 2 in the transponder doesnot include a radar mode in which automatic. frequency control AFC wouldhave to be shut down.

Due to the use of this combined radar/data transmission system, a costreduction in production is achieved in comparison with previous separatesystems, and furthermore, the reliability of transmission between thevehicle and the transponder is increased. Due to the implementat ion ofthe intermediate frequency common to both transceiver units, which maybe processed using inexpensive standard components, the describedexemplary data transmission device according to the present inventionmay be integrated easily and inexpensively into the existing automotiveradar system.

What is claimed is:
 1. A device for data transmission for at least oneof in a first motor vehicle and from a second motor vehicle, comprising:a first transceiver unit located with the first motor vehicle, and beingradar unit equipped for distance measurement that is expanded by addinga two-channel data transmission system; at least one transponder unit;and a second transceiver unit in the at least one transponder unit andbeing spatially positioned relative to the first motor vehicle one ofarbitrarily and variably, the second transceiver unit being atwo-channel data transmission unit; wherein microwave frequencies fortwo-channel communication are selected so that their difference yieldsan intermediate frequency that is processable in a heterodyne receiverin a reception part of each of the first transceiver unit and the secondtransceiver unit.
 2. The data transmission device of claim 1, furthercomprising: at least one antenna for at least one of transmitting andreceiving, being circularly polarized on a side of one of the firsttransceiver unit and the second transceiver unit, and being linearlypolarized on a side of another one of the first transceiver unit andsecond transceiver unit.
 3. The data transmission device of claim 2,wherein the at least one antenna is circularly polarized on atransponder side.
 4. The data transmission device of claim 2, whereinthe at least one antenna includes a spherical directional characteristicon a transponder side.
 5. The data transmission device of claim 1,wherein the transponder unit is part of a vehicle key.
 6. The datatransmission device of claim 5, wherein the vehicle key is configuredfor keyless access to the first motor vehicle based on an identificationsignal transmitted by data transmission between the first motor vehicleand the at least one transponder unit.
 7. The data transmission of claim1, further comprising: a second transponder unit for one of telematicapplications, acquiring fees, and remote control applications.
 8. Thedata transmission device of claim 1, wherein the first transceiver unitand the second transceiver unit each include a transmitter and areceiver configured so that their transmission frequency issimultaneously used as a local oscillator frequency for a mixer thatdownmixes a receiving frequency in a reception case.
 9. The datatransmission device of claim 1, wherein a transmission frequency and areceiving frequency of both the first transceiver unit and the secondtransceiver unit are selected so that their frequency shift conforms toband limits of a used frequency band.
 10. The data transmission deviceof claim 1, wherein the first transceiver unit and the secondtransceiver unit each include a microwave oscillator that includes adielectric resonant oscillator.
 11. The data transmission device ofclaim 1, wherein the first transceiver unit and the second transceiverunit each include a microwave oscillator that includes avoltage-controlled oscillator.
 12. The data transmission device of claim1, wherein a frequency drift is correctable by an AFC circuit in onlyone of the first transceiver unit and the second transceiver unit tomaintain a constant intermediate frequency.
 13. The data transmissiondevice of claim 12, wherein the AFC circuit is provided only in thesecond transceiver unit.
 14. The data transmission device of claim 1,wherein a fluctuation in an intermediate frequency caused by a frequencydrift is compensated in only one of the first transceiver unit and thesecond transceiver unit, and the intermediate frequency is downmixedwith a variable local oscillator signal to a lower constant intermediatefrequency.
 15. The data transmission device of claim 14, wherein acircuit for generating the variable local oscillator signal is providedonly in the second transceiver unit.
 16. The data transmission device ofclaim 1, wherein at least one of the first transceiver unit and thesecond transceiver unit includes a transmitting antenna and a separatereceiving antenna.
 17. The data transmission device of claim 1, whereinat least one of the first transceiver unit and the second transceiverunit includes a common antenna and a directional coupler for atransmitting/receiving branch.
 18. The data transmission device of claim1, wherein each of the first transceiver unit and the second transceiverunit include a frequency shift keying modulator.
 19. The datatransmission device of claim 1, wherein each of the first transceiverunit and the second transceiver unit include an amplitude shift keyingmodulator.
 20. The data transmission device of claim 1, wherein each ofthe first transceiver unit and the second transceiver unit include aphase shift keying modulator.